Extracorporeal photopheresis (ECP) is a form of apheresis and photodynamic therapy (PDT) where leucocytes (white blood cells) are separated from whole blood and exposed to photoactive 8-methoxypsoralen (8-MOP) as a photosensitiser and ultraviolet-A (UV-A) light before reintroduced back to the patient's circulation. ECP has for more than two decades been approved for the treatment of cutaneous T-cell lymphomas (CTCL) [1]. CTCL represents a heterogenous group of non-Hodkin's lymphoma while GVHD is a complication that can occur after stem cell or bone marrow transplantation in which immune cells attack the transplant recipient's body.
In addition, a number of T-cell-mediated diseases are being explored as suitable indications for ECP, including cGvHD, rejection of transplanted organs and certain autoimmune disorders. Today Therakos Photopheresis System, a device designed for this modality by the Therakos, Inc., is used at more than 150 university medical centers in US and Europe with more than 250,000 treatments so far.
Briefly, the basic procedure of ECP starts with an insertion of an intravenous line into a patient's arm. About 500 mL of blood (10% to 15% of the whole blood) are then withdrawn and collected with an anticoagulant in the Therakosis Photopheresis System. The white blood cells (mainly lymphocytes) are separated by centrifugation over a number of cycles. The leukocyte rich fraction is then treated with a sterile solution of 8-MOP as a photosensitiser and exposed to UVA irradiation, followed by returning the treated leukocytes to the patient. Red blood cells and plasma are returned to the patient between each cycle [2, 3].
In CTCL 8-MOP is thought to bind covalently to DNA in the separated leucocytes resulting in cell cycle arrest and apoptosis. However, risk of the development of cutaneous malignances after the use of psoralens under the conditions of PUVA (psoralen plus UV-A) therapy has been suggested [4]. 8-MOP binds to DNA of not only neoplastic cells, but also normal cells, thus increasing potential risk of carcinogenesis. Moreover, 8-MOP induces cell death to both tumour and normal cells with no selectivity after UV-A light exposure. In addition, the exclusive use of UV-A light to photoactive 8-methoxypsoralen (8-MOP) as a photosensitiser is under certain circumstances also potentially disadvantageous due to health risks carried by use of UV light.
It was thus the basic intention of this invention to improve on this situation and find one or more substitutes for 8-MOP for use in ECP.
This invention is based on the finding that compounds traditionally used in ECP can be replaced by a photoactivatable Porphyrin-Derivative. It was thus found that Hexaminolevulinate(HAL)-induced protoporphyrin-IX, a potent photosensitiser, localises outside of cell nucleus and that in a HAL-mediated photodynamic therapy activated/transformed lymphocytes are selectively destroyed and that this therapy induces systemic anti-tumour immunity. In addition, in a HAL-mediated photodynamic therapy it is possible to use UV-A and “blue” (visible) light leading to induction of both apoptosis and necrosis, whereas traditional 8-MOP therapy uses only UV-A and induces apoptosis only. Finally, a HAL-mediated photodynamic process using UV-A light clearly kills lymphocytes from GvHD and CTLC patients more efficiently than 8-MOP. Accordingly, 8-MOP can be replaced in ECP by photoactivatable Porphyrin-Derivatives and thus also by HAL (that induces synthesis of a protoporphyrin-IX).